Tyson Fury takes a detour from his heavyweight world-title duties when he faces MMA star Francis Ngannou on Saturday in Saudi Arabia.
The Briton welcomes former UFC heavyweight champion Ngannou to the world of boxing, in a non-title heavyweight bout overseen by the British Boxing Board of Control.
Ngannou, 37, is a massive underdog against the unbeaten WBC champion, but Fury's belt is not on the line in this encounter.
Fury says the world should "laugh" at him if he loses.
How seriously is Fury taking Ngannou?
Fury vows to knock Ngannou 'spark out' in chaotic news conference
From san quarries to fighting the Gypsy King - the rise of Ngannou
Here are predictions from some big names in the world of boxing and MMA.
UFC heavyweight Tom Aspinall: "I think Ngannou's got a chance. It's heavyweights, they punch really, really hard, especially someone like Ngannou. But as far as chances, I think it's a slim one. I think 99 times out of a 100, Fury is going to school him."
Two-weight boxing world champion Natasha Jonas: "If I was Tyson's manager and was advising him, I'd say get a bit of ring rust off, get a couple of rounds. Every now and again, put it on him and show him this is boxing. That you're the daddy. You're the king of the ring. Then get him out of there."
Former boxing world champion Joe Calzaghe: "I think Tyson Fury in a few rounds. Maybe for a couple of rounds he'll be jabbing and moving but I think rounds three or four."
UFC fighter Lerone Murphy: "Tyson Fury's going to outskill him by far. I think it's a totally different game and in the big gloves, I don't know if Ngannou is going to carry that same sort of power."
Former super-featherweight world champion Barry Jones: "Francis is the best at what he does at his weight and his chosen field. But that's not boxing. Tyson is clearly the number one in the division and doesn't have much trouble with the best active boxers, so having a problem with a guy who has never boxed before seems a bit extreme. I feel Tyson will comfortably play with Ngannou and get rid of him mid-rounds or go all out early and get rid of him as early as he can. The only question will be how good is the chin as Francis Ngannou."
Professional boxer Tommy Fury: "That's a similar affair to what I've had with KSI. That's all that is. It's a crossover fight, it's good for the fans. That's it. Again, how can you compare Ngannou with Tyson? One of the best boxers, if not the best boxer in history, to do it against an MMA guy. You can't compare the two. We all know what's going to happen in that fight. It's just what it is. It's a fan-friendly fight and then he'll move on to serious business in December."
Bellator fighter Leah McCourt: "It's hard to bet against Tyson Fury but Francis is a true champion and has done the impossible before. He looks like he has been preparing in every way he can for this fight. What I would love to see is some of these boxers take to the MMA cage though!"
Former super-middleweight world champion Richie Woodhall: "I think Tyson Fury wins this fight when he decides to. I don't give Francis Ngannou much of a chance. I think the first three rounds will be crucial for Ngannou to get the win. There's no way he can beat Fury on points - he's not used to 10 rounds, he's not used to professional boxing. I can honestly see Fury playing the game for a little while and then when he wants to finish it, I'll be very surprised if it goes beyond six rounds."
American heavyweight Jared Anderson: "If I had to guess I'd go with Tyson Fury. I'm a huge Tyson fan, and I hope Mike Tyson did his best with Francis Ngannou to help him get past the length, but I've got Fury beating him by a large margin."
Former UFC heavyweight champion Junior dos Santos: "It's going to be a great show but I see Tyson Fury doing what he does best, moving around, throwing jabs, and little by little, taking the fight. But I'm rooting for Francis Ngannou. Of course I want the MMA world to have their first victory over the boxing world. He has the power, he's maybe the hardest hitter ever in MMA. We have little chances so let's go for it."
Boxing world champion Nina Hughes: "Comfortable win for Fury. Plays with him in the early rounds, ending with Fury knocking him out later in the fight."
British heavyweight Frazer Clarke: "It's such a huge night of boxing but the main event doesn't involve two boxers. It shows you where boxing is at the minute. I think there can be only one winner - Tyson Fury. Francis Ngannou may have a puncher's chance but it's a very small puncher's chance. It's a great card with heavyweight bouts but the main event should be a foregone conclusion."
Former lightweight world champion Anthony Crolla: "If Ngannou does it, I genuinely think it would be one of the biggest upsets in sporting history, not just boxing. The fight lasts as long as Fury wants it to last. A big thing will be if this [Oleksandr] Usyk fight is made for 23 December, then he won't want to take too many chances. So I see it being over in three rounds. I'm expecting him to dance about, poke and break Ngannou down. Maybe even let Ngannou let some shots go and show him elusive he is. But I reckon Fury will get him out of there by the halfway mark. I'll be really surprised if it goes past that."
Former light-middleweight world champion Hannah Rankin: "I have Fury winning this fight with the far superior boxing ability. I think he is approaching this fight seriously as Ngannou does have power in his punches, if not the same boxing ability, and Fury doesn't want to risk the fight with Usyk being delayed by a cut or an injury. I think he will use the fight to showcase his boxing skills and ability to a packed out crowd and no doubt there'll be some showmanship in there as well."
Former heavyweight world champion Shannon Briggs: "I'm going with Tyson Fury in round five. He'll outbox him for a couple of rounds, then Francis Ngannou is going to make a mistake, and Fury will put him to sleep."
Former British UFC welterweight Dan Hardy: "I think Fury is going to play with this fight for the first three rounds, make Ngannou tired, and then look to take him out in the fourth, fifth and sixth round. Uppercuts and body shots will be key. But I'm here to be surprised and I'm ready for Ngannou to land a shot which will change the look of this fight."
British boxer John Ryder: "Tyson Fury plays with Ngannou until he fancies ending it and then obliterates him. He'll make a show of it for a while, but there's only one winner and that's Tyson Fury."
UFC fighter Nathaniel Wood: "Unfortunately, I'm going to have to say Ngannou doesn't have a chance in a boxing match. Maybe a slight chance, because it is the heavyweight division. But he's fighting the best boxer in boxing, it's a completely different sport. I'm hoping he pulls it out of the bag. That would be amazing and show people us MMA fighters can box too."
